Precast concrete structural panels and beams having reinforcing ribs are known in the art. Such panels are typically prepared by casting both the flat slab portion of the panel and the reinforcing ribs in a single mold at the same time with pretensioned reinforcing rods being present in the ribs and the slab itself.
Such precast reinforced panels have certain inherent deficiencies however. Since the entire panel is cast in a single mold at a single time, there is an obvious lack of versatility or ability to alter the size and configuration of the panel. Either the panel must be used in the size and configuration in which it is cast or a number of different molds provided so that different size panels of different configuration can be prepared. Obviously this is expensive and beyond the means of most fabricating units.
Further, since the ribs which reinforce the flat slab of the panel contain tendons or wires which are under tension at the time the unit is cast, subsequent relaxation of this tension frequently produces a camber or bowing in the panel. This is of course undesirable where a perfectly flat surface is required.
Typically, also, when precast and pretensioned structural panels having reinforcing ribs are fabricated, the portion of the mold which forms the reinforcing ribs is on the bottom of the mold unit and the concrete is poured first into the molds for the ribs and then after these molds are filled into the rest of the mold to form the slab itself. Thus, the panel is in effect cast "bottom up" with the bottom surface of the panel facing up which requires that it subsequently be finished or smoothed to the desired texture.